1. Field of the Invention
The present invention relates to a method for choosing a network element of a mobile telecommunication network from a plurality of network elements in order to provide a predetermined service and a mobile telecommunication network which is adapted to executing the method.
2. Description of the Related Art
A mobile telecommunication network includes a radio access network (RAN), a core network (CN) and user equipment (UE). The core network is responsible for switching and routing calls and data connections to external networks. The radio access network handles all radio-related functionalities. The user equipment is the interface between a user and the mobile telecommunication network.
A mobile telecommunication network must provide for a paging functionality. To this end a paging channel (PCH) is established. The paging channel is a downlink transport channel that carries data relevant to the paging procedure, i.e., when the network wants to initiate communication with a terminal. The simplest example is a speech call to the terminal.
The radio access network (RAN) is composed of nodes B, respectively base stations, and radio network controllers (RNC). A predetermined number of base stations are connected to a single radio network controller. The radio network controller (RNC) owns and controls the radio resources and its domains (the base stations connected to the RNC). The radio network controller (RNC) is at the same time the service access point for all services, which the radio access network (RAN) provides to the core network (CN). The base stations interface with the user equipment. The base stations are basically radio transceivers, which are distributed across the territory, in which mobile telecommunication services are to be provided. The user equipment normally corresponds to a mobile telephone. Due to the limited range of the base stations, the user equipment may only communicate with a selected number of base stations within its range.
In order to communicate with the user equipment, the location area must be known. The location area is a grouping of adjacent base stations. If the mobile telecommunication network did not have information about the position of the user equipment, then a paging message would have to be transmitted by all the base stations in order to ensure communication with the user equipment. Thanks to the location areas, the mobile communication network knows the position of the user equipment with reasonable precision and therefore the paging message must be transmitted only by a small group of base stations. Whenever the location area (LA) of user equipment changes, this change must be signaled to the network via a location update procedure. The location area is registered within the mobile services switching center/visitor location register (MSC/VLR) for circuit switched connections and the routing area (RA) is registered in the serving GPRS support note (SGSN) for packet switched communication. The MSC/VLR and the SGSN form part of the core network of the mobile telecommunication network. Each SGSN and each MSC/VLR are connected to several radio network controllers (RNC). For packet switched connections information is transmitted via the SGSN to the radio access network (RAN). For circuit switched connection the MSC/VLR is responsible for transmitting messages to the radio access network. The SGSN or the MSC/VLR selects the radio network controller (RNC) and the associated base stations for transmitting the paging message to the user equipment using the mapping of the location area and the user equipment.
The paging procedure, according to the state of the art, has several drawbacks, in particular the SGSN and MSC must perform many tasks for paging. Consequently, the MSC and SGSN are very complex. The SGSN or MSC need to know in advance the configuration of the network. The core network elements SGSN and MSC need to be able to select the radio network controllers for paging a message. Any changes to the network, in particular adding or removing radio network controllers (RNC), require changes to the SGSN and MSC. In order to coordinate paging for circuit switched (CS) and packet switched (PS) services an additional interface (Gs interface) between the SGSN (Serving GPRS Support Node) and the MSC (Mobile Switching Centre) has to be defined. Paging coordination means that the network sends paging messages for CS services on the same channel as used for PS services and vice versa. Furthermore, a mapping between the user equipment and the radio network controllers (RNC) connected to the SGSN or MSC has to be provided within the SGSN or MSC. The SGSN or MSC must be able to choose the appropriate RNC using the mapping.